The Lactate Threshold

If VO2 max is your aerobic endurance potential then your lactate threshold plays a significant role in how much of that potential you are tapping.

Lactate threshold has been defined as:

The point during exercise of increasing intensity at which blood lactate begins to accumulate above resting levels, where lactate clearance is no longer able to keep up with lactate production. (3)

During low intensity exercise, blood lactate remains at or near to resting levels. As exercise intensity increases there comes a break point where blood lactate levels rise sharply (4,5). Researchers in the past have suggested that this signifies a significant shift from predominantly aerobic metabolism to predominantly anaerobic energy production.

Several terms have been used to describe this shift and many coaches and athletes believe it is the same phenomenon:

Lactate threshold

Anaerobic threshold

Aerobic threshold

Onset of blood lactate accumulation (OBLA)

Maximal lactate steady state

Although these terms are used interchangeably, they do not describe the same thing. Lactate accumulation only determines the balance between lactate production and its clearance and suggests nothing about the availability or lack of oxygen so the terms aerobic and anaerobic become a bit misleading.

The reasons for lactate accumulation are complex and varied and not yet fully understood. For more information on this topic see the lactic acid article.

OBLA
At a slightly higher exercise intensity than lactate threshold a second increase in lactate accumulation can be seen and is often referred to as the onset of blood lactate accumulation or OBLA. OBLA generally occurs when the concentration of blood lactate reaches about 4mmol/L (6,7). The break point that corresponds to lactate threshold can often be hard to pinpoint and so some Exercise Physiologists often prefer using OBLA.

Maximal Lactate Steady State
Maximal lactate steady state is defined as the exercise intensity at which maximal lactate clearance is equal to maximal lactate production (8). Maximal lactate steady state is considered one of the best indicators of performance perhaps even more efficient than lactate threshold (8,9).

Lactate Threshold as a Percentage of VO 2 Max

The lactate threshold is normally expressed as a percentage of an individuals VO2 max. For example, if VO2 max occurs at 24 km/h on a treadmill test and a sharp rise in blood lactate concentration above resting levels is seen at 12 km/h then the lactate threshold is said to be 50% VO2 max.

In theory, an individual could exercise at any intensity up to their VO2 max indefinitely. However, this is not the case even amongst elite athletes. As the exercise intensity draws closer to that at VO2 max, a sharp increase in blood lactate accumulation and subsequent fatigue occurs the lactate threshold is broken. In world-class athletes lactate threshold typically occurs at 70-80% VO2 max. In untrained individuals it occurs much sooner, at 50-60% VO2 max (10,11).

Generally, in two people with the same VO2 max, the one with a higher lactate threshold will perform better in continuous-type endurance events. See the graph below:

Although both Athlete 1 and Athlete 2 reach VO2 max at a similar running speed, Athlete 1 has a lactate threshold at 70% and Athlete 2 has a lactate threshold at 60%. Theoretically, Athlete 1 can maintain a pace of about 7.5 mph (12 km/h) compared to Athlete 2s pace of about 6.5 mph (10.5km/h).

VO2 max has been used to predict performance in endurance events such as distance running and cycling but the lactate threshold is much more reliable. Race pace has been closely associated with lactate threshold (11).

Lactate Threshold and Training

With training, lactate threshold as a percentage of VO2 max can be increased. Even if there are no improvements in maximal oxygen uptake, increasing the relative intensity or speed at which lactate threshold occurs will improve performance. In effect, proper training can shift the lactate curve to the right:

Following training, the reductions in lactate concentration at any given intensity may be due to a decrease in lactate production and an increase in lactate clearance (12). However, Donovan and Brooks (13) suggest that endurance training affects only lactate clearance rather than production.

Blood lactate levels after an intense exercise bout are also lower following training. For example, immediately after a 200m swim at a fixed pace, blood lactate may be as high as 13-14 mmol/L. Following 7 months of training these levels can decrease to under 4mmol/L (14). Before training, a swim leading to such high levels of lactate would force the swimmer to slow down dramatically or stop after the 200m. But following training, lactate levels of under 4mmol/L would probably allow the swimmer to continue after 200m, at the same pace, indefinitely.

Studies have shown that training at or slightly above the lactate threshold can increase the relative intensity at which it occurs (4,13). For more information and sample training sessions for improving lactate threshold see the lactate threshold training article.